Retort Furnace for Heat Treating Metal Workpieces

ABSTRACT

In a retort furnace having a heating assembly, a circulation unit, and an assigned cooling unit, uniform and rapid cooling of the heat-treated workpieces is achieved by three solution variants. The first variant includes a second floor ( 9.1 ) assembled to a floor ( 9 ) to form an intermediate space which is divided into two ring spaces which are isolated gastight from one another including a first volume space ( 16 ) and a second volume space ( 17 ). The second variant includes situating throttle valves ( 20, 21 ) in a housing ( 36 ), each valve having a receptacle space ( 33 ), into which a valve plug is movable. In the third variant which is a combination of the first and second variants, the first volume space ( 16 ) and the second volume space ( 17 ) are adapted to interact for flow technology in such a manner that in the open position of the plug, the flow cross-section of each line ( 11, 14 ) is completely unblocked and provides circulation of a cold gas with favorable flow and therefore rapid cooling of the batch ( 7 ).

CROSS REFERENCE TO RELATED APPLICATIOS

This application is a Division of International Application No. PCT/DE2009/000963 filed Jul. 13, 2009 which designates the United States. The entire disclosure of said international application is incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a retort furnace for the heat treatment, for example, for the blank annealing, annealing under nitrogen or nitrogen/hydrogen, nitriding, or nitrocarburizing of metal workpieces, the retort furnace essentially comprising a furnace housing having a retort, a heating unit, a circulation unit, and an assigned cooling unit and the retort, which is enclosed by a furnace housing, is implemented as cylindrical and is closed gastight at one end using a floor and having a flow connection to at least two gas-conducting lines, which are closable using throttle valves, and which are in turn connected to the cooling unit.

2. Description of the Related Art

Retort furnaces for the heat treatment of metal workpieces are known according to the prior art in manifold configurations, for example, according to DE-AS 2 010 433, DE-OS 27 54 034, DE 30 28 952 C2, DE 31 43 532 A1, DE 36 31 389 C2, and DE 103 38 431 A1.

Primarily increasing the efficiency of the heat treatment has already been proposed many times for retort furnaces. However, in retort furnaces, after the uniform heating to be achieved of the workpieces to be heat-treated, the subsequent uniform and intensive cooling of the workpieces also has a special significance, which is to be studied in greater depth because of the treatment step, which is unproductive per se.

Retort furnaces for the heat treatment of metal workpieces comprise a retort enclosed by a furnace housing, which is implemented as cylindrical and is closed gastight at one end using a floor. The retort also has a charging opening, which is used for the purpose of placing the workpieces to be heat-treated into the retort or removing the heat-treated workpieces from the retort through the charging opening. The charging opening is closable gastight using a cover, which is preferably implemented as pivotable.

The furnace housing typically provides a volume space. The retort itself is situated within this volume space, which in turn provides a volume space, that functions as the actual heat treatment space. In addition to the retort, heating elements are additionally also provided within the volume space formed by the furnace housing, which are used for heating the retort and thus the treatment space enclosed by the retort during proper use of the retort furnace.

The heat treatment of a workpiece typically occurs in a gaseous atmosphere. The retort therefore preferably has connecting pieces on the floor side, which allow the connection of gas-conducting lines. Gases and/or gas mixtures may be introduced alternately into the treatment space defined by the retort through these lines. Such gases may be treatment gases, oxidation gases, coolant gases, and/or corresponding gas mixtures, for example.

During performance of a proper method for the heat treatment of metal workpieces, it is typically provided that a method step of workpiece heating is followed by a method step in which the workpieces are held at one or more temperature levels—as a function of the heat treatment—and finally a method step of workpiece cooling follows.

Efforts are taken both during the heating and also during the cooling to perform the workpiece heating or cooling as rapidly and uniformly as possible. During the holding phase at an established temperature level, efforts are taken for the greatest possible temperature uniformity of the workpieces within the batch, as well as the most uniform possible availability of the gases at every point of the batch. For this purpose, the atmosphere located in the interior of the gastight closed retort is circulated. This is performed using a circulation unit, which is typically situated in the interior of the retort.

In order to achieve improved circulation and uniformity of the furnace atmosphere and temperature, using so-called gas conduction cylinders is also known from the prior art, which ensure forced guiding of the furnace atmosphere in combination with the circulation assembly.

Furthermore, it may be determined according to the prior art that the retort has a flow connection to at least one gas-conducting line, this line being closable using one or more so-called throttle valves. Thus, for example, to cool the workpieces, gas may be suctioned out of the retort via a gas-conducting line, conducted through a cooling unit, and returned into the retort via a second gas-conducting line.

During performance of a proper method for the heat treatment of metal workpieces using an above-described retort furnace, it may be necessary to isolate the gas-conducting lines in relation to the retort interior, in order to prevent gases from entering the retort interior or the gas atmosphere located in the retort interior from exiting via the gas-conducting lines. In order to implement an isolation of the gas-conducting lines in relation to the retort interior, the throttle valves are known from the prior art, which are implemented as discs situated so they are pivotable in the respective gas-conducting line. These discs are rotatable by at least 90° and may thus be brought into an open or closed position. In the closed position, the flow cross-section of the gas-conducting line is essentially closed, so that an isolation of the gas-conducting line to the retort interior is achieved. In the open position, the flow cross-section of the gas-conducting line is essentially released, so that a flow connection is formed between the gas-conducting line, on the one hand, and the retort interior, on the other hand.

The throttle valves previously known from the prior art also have apparently proven themselves for closing the gas-conducting lines having a flow connection to the retort of the retort furnace, but a need exists for improvement in particular with respect to their more functional handling and flow configuration.

In addition, a heat treatment furnace, in particular a pressure sintering furnace having a furnace housing, an insulation cage, which is held by the furnace housing and forms a boiler chamber, and a muffle, which is situated in the interior of the insulation cage, envelops the workpiece batch, and delimits an insulation space within the insulation cage, is described in DE 103 12 650 B3. It comprises a device for the introduction of coolant gas from a gas supply container into the spaces delimited by the furnace housing, the insulation cage, and the muffle.

This heat treatment furnace is to be improved in such a way as to achieve accelerated cooling of the batch with its closed insulation and closed muffle and furthermore be able to cool an individual furnace area separately through targeted inflow and circulation flow. The heat treatment furnace was designed so that if needed it can switch over to an external cooling unit having a heat exchanger and additional fan. For this purpose, a multiway or multichannel valve having a valve housing guided through the insulation cage and the muffle, having at least three gas outlet openings, is provided. Parts of the insulation cage and the muffle, which are linked to the furnace housing and are closable in relation to the front walls of the furnace housing, were situated on the respective diametrically opposing front walls of the insulation cage and the front walls of the muffle.

If a person skilled in the art views this embodiment with respect to the transmission of retort furnaces according to the species of the type described at the beginning, uniform cooling, which is as rapid as possible, of the heat-treated workpieces is unproductive and requires complex devices if a gas flow must be suctioned out of the retort, conducted via an external cooling unit, and subsequently returned back into the retort.

BRIEF SUMMARY OF THE INVENTION

An object of the invention is to achieve, in retort furnaces according to the present invention and of the type described above, uniform cooling of the heat-treated workpieces, which occurs as rapidly as possible, because the cooling is a necessary, but fundamentally unproductive method step.

Since a gas stream is suctioned out of the retort, conducted via an external cooling unit, and subsequently returned back into the retort to cool the workpieces, it is necessary to circulate the cold gas as quickly as possible and to avoid resistances which obstruct the cooling gas volume flow.

For this purpose, on the one hand, the formation of a second floor of the retort and/or, on the other hand, the valves for the functionally-reliable closing of the gas-conducting lines connected to the retort of the retort furnace are to be altered in their design in such a manner that more favorable flow conditions result overall.

This is achieved according to the present invention by three unified variants of the invention, which achieve the objects and may be implemented in combination with one another.

According to the first variant, it is provided that in a retort furnace for the heat treatment of metal workpieces, the floor comprises a second floor to form an intermediate space, i.e., the retort is implemented as double-walled, and this intermediate space is divided into a first volume space and a second volume space preferably configured as two (concentric) ring spaces which are isolated gastight from one another. The first volume space is connected to the first gas-conducting line and second volume space is connected to the second gas-conducting line, whereby the circulation of the cold gas using a coolant volume flow having favorable flow whereby the cooling of the batch may be accelerated.

According to the second variant, the retort furnace according to the present invention is implemented so that the first and second throttle valves each include a housing comprising a receptacle space, into which a valve plug is movable in such a manner that the flow cross-section of each gas-conducting line is completely unobstructed or unblocked in the open position of the respective plug, a formation of the receptacle space having favorable flow is provided, and a gaseous volume stream can be conducted with favorable flow in each gas-conducting line.

The third variant combines the first and second variants in the meaning of a functional combination of their advantageous features and functions to form an overall effect, in that the retort furnace combines

-   -   the feature group, in which the floor comprises a second floor         to form an intermediate space, this intermediate space being         divided into a first volume space and a second volume space         preferably configured as two ring spaces, which are isolated         gastight from one another, and the first volume space is         connected to the second gas-conducting line and the second         volume space is connected to the first gas-conducting line,     -   with the feature group, in which the first and second throttle         valves each include a housing comprising a receptacle space,         into which a valve plug is movable in such a manner that the         flow cross-section of each line is completely unblocked when the         plug is in the open position,     -   in such a manner that the first volume space and the second         volume space, in flow interaction with the functions of the         respective valve plugs, which completely unblock the flow         cross-section of each gas-conducting line when in the open         position, result in circulation of the cold gas with favorable         flow and therefore rapid cooling of the batch.

In the first and third variants, the outer diameter of the second floor of the floor is dimensioned smaller than the inner diameter of the retort.

Furthermore, the first volume space can have a flow connection via the second gas-conducting line to an external coolant gas fan and the second volume space can have a flow connection via the first gas-conducting line to an external cooler, whereby the hot gas located in the retort can be evacuated and transferred to the external cooler.

The second volume space can advantageously be connected to suction pipes, which are connected to the treatment space enclosed by the retort.

Further, the first and second variants are realized by the first volume space and the second volume space being separated gastight by a ring, which can be incorporated in manufacturing in a favorable manner by welding, for example, into the two ring spaces isolated gastight from one another.

In the second and third variants, the valve plug which is movable into the receptacle space of the housing of each throttle valve has a pivot arm, which is situated so it is pivotable on a holding arm around a pivot point.

The pivot arm can be connected to the holding arm so it is pivotable through an angle of greater than about 90° and is expediently connected to a drive mechanism such as a pneumatic positioning cylinder.

The valve housing is removably connected to one of the gas-conducting lines so it is replaceable. The connection includes a first flange connection and a second flange connection. The valve housing has an installation opening that is closable by means of a cover for favorable installation.

The valve drive mechanism can advantageously be mounted on the valve cover, the cover having a gastight passage for the piston rod, which is linked using a coupling element to a piston rod and an oblong hole of the pivot arm to actuate the valve plug. The holding arm can be functionally attached on the valve cover.

The stated object is achieved optimally with respect to the overall improved flow conditions in the retort furnace by the implementation according to the invention of one floor of the retort, in that this one floor of the retort is implemented as double-walled to form a volume space and is divided into two ring spaces isolated gastight from one another, and the altered design principle according to the invention, that the gas-conducting lines are closable using the throttle valves and are connected to the valve housing which has a receptacle space, into which the plug is movable, so that the flow cross-section of the line is completely unblocked when the plug is in the open position.

Success is also achieved with the double-walled floor implementation, since the cold gas is thus better circulated and extraordinarily good circulation of the furnace atmosphere is provided, and therefore substantial flow through the workpieces to be heat-treated is advantageously provided.

On the other hand, more favorable flow conditions are also provided overall for the cold gas solely with the altered plug movement in the throttle valves.

However, in the combined embodiment, the double-walled floor implementation and the altered valve plug movement are functionally combined in their flow effect with one another.

It is to be emphasized that a coolant gas or a coolant gas mixture can be fed into the outer ring space from the outside using the external coolant gas fan.

The inner ring space has a flow connection to the actual treatment space of the batch, which is enclosed by the retort. For this purpose, the suction pipes are provided, which form a flow connection from the inner ring space to the treatment space of the retort.

Coolant gas fed into the outer ring space can also flow through openings into the treatment space enclosed by the retort. The connection openings are dimensioned as a function of the cooling fan power in such a manner that the coolant gas located in the outer ring space can exit at comparatively higher speed from the openings and enter into the treatment space enclosed by the retort

The passage openings forming a flow connection from the outer ring space to the treatment space of the retort are preferably implemented at the front of the inner wall of the double-walled floor, i.e., between an inner wall, on one side, and the lateral surface of the retort, on the other side.

This embodiment can be achieved, for example, in that the external diameter of the retort-side wall, i.e., the inner wall of the double-walled floor, is implemented as smaller than the internal diameter of the retort, as a result of which an annular gap results between the inner wall of the double-walled floor, on one side, and the inner side of the lateral surface of the retort, on the other side. This annular gap can be divided into individual passage openings, which results, for example, in that the inner wall of the double-walled floor is frontally connected, for example, by welding, to the lateral surface of the retort at specific intervals

The above-described design of the annular gap, i.e., the passage openings which form a flow connection of the outer annular space to the treatment space of the retort, has the advantage that coolant gas inflowing via the outer ring space is introduced into the treatment space of the retort in direct proximity to the retort jacket and parallel thereto.

In this way, extraordinarily good flow through a workpiece batch located in the retort is achieved overall, which correspondingly results in very good heat transfer between gas stream, on the one hand, and workpiece batch, on the other hand.

The above-described design allows the hot gas located in the retort, i.e., the hot atmosphere located therein, to be suctioned off using the suction pipes connecting the volume space enclosed by the retort, the suctioned gases, i.e., the suctioned atmosphere, being exhausted through the inner annular space of the double-walled floor of the retort.

The inner ring space is connected to the cooler for the purpose of suctioning. The suctioned gases are guided through the cooler and caused to cool. The reuse of this gas, i.e., the former treatment atmosphere, is possible, preferably as a coolant gas which is supplied back to the outer ring space of the double-walled floor of the retort. This can be performed using support of the mentioned coolant gas fan.

The coolant gas conveyed into the outer ring space exits back into the useful space, i.e., the treatment space of the retort, and preferably close to the retort jacket, so that the inflowing coolant gas is force-guided close to the inner side of the lateral surface of the retort and parallel thereto. As a result, a flow results in the interior of the retort, which is distinguished in that hot gases or hot furnace atmosphere is exhausted from the inner area of the volume space enclosed by the retort, and coolant gas is simultaneously conducted into the outer edge area of the volume space enclosed by the retort, so that a flow circulation results in the retort, as an addition of the volume flows of the external cooling fan, on the one hand, and the circulation unit located in the retort, on the other hand. As a result of this flow circulation, an improved gas flow through the workpiece batch located in the retort results in comparison to the known furnaces, and which results in better heat transfer between workpiece batch and gas or gas mixture, i.e., more rapid cooling of the batch.

The above-described design can be utilized in retort furnaces in general use, i.e., it is usable for both horizontal and also vertical retort furnaces.

These advantageous functions support the design according to the invention of the throttle valves, which is provided for an expansion in the form of a housing, having an internal receptacle space. The valve plug is movable into the receptacle space, and in such a manner that the cross-section of the gas-conducting line is completely unobstructed when the plug is in the open position.

This design advantageously allows unnecessary flow resistances to be avoided, in contrast to the previously known throttle valves. Upon opening of a rotating valve known from the prior art, it advantageously pivots from a transverse position into a lengthwise position, in which it at least partially still blocks the flow cross-section of the gas-conducting line, however.

This disadvantageously results in an unnecessary flow resistance, which results in throttling of the performance of the gas fan connected to the gas-conducting line and therefore a reduction of the gas volume flow.

In the design according to the present invention, these disadvantages are overcome, since the valve plug is moved in the open position into the receptacle space of the valve housing, whereby the flow cross-section of the gas-conducting line is completely unblocked and the occurrence of unnecessary flow resistances is entirely prevented.

According to the invention, it is provided that the valve plug is implemented as pivotable. Accordingly, the movement of the cover occurs as a pivot movement into the receptacle space of the valve housing. This pivoting ability of the cover can be implemented, for example, by having the plug situated on a pivot arm and the pivot arm is articulated on a holding arm, for example

The pivot arm and therefore the plug situated thereon may thus be pivoted easily in relation to the holding arm. A pivot movement of the pivot arm through an angle of at least 90°, and preferably at least through 95°, is thus provided.

An at least theoretical pivoting ability of greater than 90° offers the advantage that the plug can be pressed with a certain contact pressure against a connecting piece of the gas-conducting line, which causes a gastight closure of the gas-conducting line in particular in combination with a seal provided on the line and/or cover. Such a gastight decoupling of gas-conducting line, on the one hand, and retort inner space, on the other hand, is not possible with the closure valves used as the valve plug according to the prior art, because a ring gap always remains between the inner side of a gas-conducting line, on the one hand, and the closure valve, on the other hand, due to manufacturing tolerances, occurrences of wear, and/or differing thermally related expansions.

According to one implementation of the valve plug, it is provided that the pivot arm is linked to a positioning cylinder. Using this positioning cylinder, pivoting of the pivot arm in relation to the holding arm can be caused. The positioning cylinder preferably operates pneumatically. However, other designs are also possible, for example, hydraulically or mechanically operating positioning cylinders or actuators.

Because of this embodiment, the valve plug itself can advantageously also be installed in the course of a retrofit. The throttle valves are installed in a simple way between the flange connections of the gas-conducting lines as an intermediate element.

According to the invention, the valve housing has an installation opening. This also allows later access to the adjustment mechanism of the valve plug, i.e., in particular the pivot arm and the plug itself and optionally also the positioning cylinder. Removal, repair, or other later work is thus easily performed.

The installation opening is preferably closable gastight using a correspondingly implemented cover.

It is optimal if the double-walled floor implementation and altered plug movement are used in combination in a retort furnace, because the object of the invention, of achieving uniform and intensive cooling of the heat-treated workpieces in retort furnaces according to the species, circulating the cold gas better, and preventing unnecessary resistances which obstruct the coolant volume flow, is thus maximally achieved.

Both the implementation of the floor of the retort according to the invention and also the throttle valves for the functionally reliable closing of the gas-conducting lines, which are connected to the retort of the retort furnace, for the cold gas therefore provide more favorable flow conditions overall, which cause more rapid cooling of the batch.

BRIEF DESCRIPTION OF THE VIEWS OF THE DRAWINGS

In the associated drawings of an exemplary embodiment of the invention, in the figures:

FIG. 1 shows the view in a section of a retort furnace according to the invention,

FIG. 2 shows an enlarged section view according to FIG. 1 showing the double-walled implementation according to the invention of the floor 9 by the second floor 9.1, and

FIG. 3 shows the view of a throttle valve according to the invention as a detail in longitudinal section

DETAILED DESCRIPTION OF THE INVENTION

FIGS. 1 and 2 show a schematic view of a retort furnace 1 according to the invention in longitudinal section. The retort furnace 1 is equipped in the exemplary embodiment shown with horizontally oriented retort 3, i.e., a horizontal retort furnace 1.

The retort furnace 1 has a furnace housing 2. This housing encloses a first volume space 4, within which, the retort 3, a heating assembly 5, and other features are situated. The furnace housing 2 accordingly receives the retort 3 and the heating assembly 5.

The retort 3 is implemented as a cylindrical hollow body. This hollow body is closed gastight at one end using a floor 9. The retort 3 has a charging opening 10 opposite to the floor 9, which is closable gastight using a cover 10.1. A second volume space 6, which represents the actual useful space, i.e., treatment space of the retort furnace 1, and which is enclosed by the retort 3, is accessible through the charging opening 10. Workpieces to be heat-treated, which are assembled to form a batch 7, for example, are placed in the retort 3 via the charging opening 10. The retort 3 is also unloaded via the charging opening 10.

The heating assembly 5 received by the furnace housing 2 is used for heating the first volume space 4, which is enclosed by the furnace housing 2, and is generally referred to as the furnace space. As a result of the heating of this furnace space, the retort 3 is heated by heat transfer, which results in heating of the batch 7 situated in the interior of the retort 3.

The heat treatment occurs under a gas atmosphere in the second volume space 6 enclosed by the retort 3. In order to achieve good circulation of the gas atmosphere and a uniform temperature within the second volume space 6, a gas flow is generated through the batch 7 using a circulation unit 8 in combination with a conduction unit 15. The conduction unit 15 is implemented as a cylindrical chamber, whereby an annular space 6.1 is formed between the inner wall of the retort 3 and the conduction unit 15. The gas flows through this ring space 6.1 in the direction of the arrows forward to the side of the cover 10.1 and subsequently through the batch 7 downward to the circulation unit 8, this flow being indicated by the further arrows.

The gases required for the heat treatment may be introduced into the retort 3 via pipes (not shown here), which have a flow connection to the floor 9. After performance of the heat treatment, the cooling of the batch 7 is performed, whose effect according to the invention by substantial novel features is to be emphasized.

Firstly, gas is suctioned from the retort 3 via a first line 11, implemented as a suction pipe, which is connected to the floor 9, through a cooler 12 using an external coolant gas fan 13 and returned back into the retort 3 through a second line 14 implemented as an inlet pipe. According to the invention, a second floor 9.1, whose diameter is smaller than the internal diameter of the retort 3, is located between the floor 9 and the circulation unit 8. A volume space is implemented between the floors 9 and 9.1, which is divided by a peripheral ring 18 into an inner volume space 17 and an outer volume space 16. The inner volume space 17 has a flow connection through suction pipes 19 to the second volume space 6, in which the batch 7 is located, and to the first line 11 forming the exhaust suction pipe. The outer volume space 16 has a flow connection to the ring space 6.1 and to the second line 14 forming the inlet pipe. In this way, hot gas is suctioned out of the treatment space 6 and cold gas is blown into the ring space 6.1. The pipes 11 and 14 are closed by means of the valve plugs 25 (FIG. 3) in the first and second throttle valves 20, 21 during the heat treatment.

The throttle valves 20, 21 are shown in greater detail in FIG. 3. They are installed in the lines 11, 14 using flange connections 23, 24. According to the invention, they have a plug 25, which closes an entry opening 26 into the lines 11, 14 completely gastight. The plug 25 is fastened so it is rotatable on a holding arm 27 about the rotation point 32. The plug 25 is fastened to a piston rod 29 of a drive 28 such as a positioning cylinder via a pivot arm 22 and a coupling element 30, which engages in an oblong hole 31 on the pivot arm 22. The plug 25 is opened or closed by respectively retracting or extending the piston rod 29. The plug 25 pivots in the open state into a receptacle space 33, the entire flow cross-section of the entry opening 26 is thus fully unblocked in the open state. Holding arm 27 and drive mechanism 28 such as a pneumatic positioning cylinder are connected to a cover 35, which can be completely removed, so that the receptacle space and the valve mechanism are freely accessible via the installation opening 34.

This exemplary embodiment comprises the novel implementation, on the one hand, using the first variant of the invention and, on the other hand, using the second variant of the invention, which are shown combined here as the third variant of the invention.

INDUSTRIAL APPLICABILITY

The effects achieved by the altered configuration of the double floor according to the invention and/or by the altered cover movement provide a substantial usage value increase to the operator of a retort furnace with respect to substantially more rapid cooling of the heat-treated workpieces.

LIST OF REFERENCE NUMERALS

-   1 retort furnace -   2 furnace housing -   3 retort -   4 first volume space -   5 heating unit -   6 treatment space -   6.1 ring space -   7 batch -   8 circulation unit -   9 floor -   9.1 second floor -   10 charging opening -   10.1 cover -   11 first line -   12 cooler -   13 coolant gas fan -   14 second line -   15 conduction unit -   16 outer volume space -   17 inner volume space -   18 ring -   19 suction pipe -   20 first throttle valve -   21 second throttle valve -   22 pivot arm -   23 first flange connection -   24 second flange connection -   25 valve plug -   26 entry opening -   27 holding arm -   28 drive/positioning cylinder -   29 piston rod -   30 coupling element -   31 oblong hole -   32 pivot point -   33 receptacle space -   34 installation opening -   35 cover -   36 housing 

1. A retort furnace (1) for the heat treatment of metal workpieces, having a cylindrical retort (3), which is enclosed by a furnace housing (2) having a heating assembly (5), and which a) encloses a treatment space (6) for a batch (7) of workpieces, b) is closed gastight at one end using a floor (9) and has flow connections to at least first and second gas-conducting lines (11, 14), which are each closable using a throttle valve (20, 21), and c) has a gastight closable charging opening (10) at the other end, wherein a gas stream can be suctioned out of the retort (3), conducted through an external cooling unit, and subsequently returned back into the retort (3), and wherein a cold gas can be circulated to cool the workpieces, and wherein the improvement comprises the floor (9) including a cylindrical second floor (9.1) that forms an intermediate space and the intermediate space is divided into two ring spaces isolated gastight from one another including a first volume space (16) and a second volume space (17), the first volume space (16) being connected to the first gas-conducting line (14) and the second volume space (17) being connected to the second gas-conducting line (11), whereby the circulation of the cold gas can be accelerated using a coolant volume flow having favorable flow and whereby cooling of a batch (7) can be accelerated.
 2. A retort furnace (1) for the heat treatment of metal workpieces, having a cylindrical retort (3), which is enclosed by a furnace housing (2) having a heating assembly (5), and which a) encloses a treatment space (6) for a batch (7) of workpieces, b) is closed gastight at one end using a floor (9) and has flow connections to at least two gas-conducting lines (11, 14), which are each closable by means of first and second throttle valves (20, 21), and c) has a gastight closable charging opening (10) at the other end, wherein the improvement comprises the first and second throttle valves (20, 21) each have a housing (36) comprising a receptacle space (33), into which a valve plug (25) is movable in such a manner that the flow cross-section of each line (11, 14) is completely unblocked in the open position of the valve plug (25), and an implementation of the receptacle space (33) for favorable flow is provided and a gaseous volume stream can be guided with favorable flow in each line (11, 14).
 3. A retort furnace (1) for the heat treatment of metal workpieces, having a cylindrical retort (3), which is enclosed by a furnace housing (2) having a heating assembly (5), and which a) encloses a treatment space (6) for a batch (7) of workpieces, b) is closed gastight at one end using a floor (9) and has flow connections to at least first and second gas-conducting lines (11, 14), which are each closable by means of first and second throttle valves (20, 21), and c) has a gastight closable charging opening (10) at the other end, wherein the improvement comprises: d) the floor (9) comprises a second floor (9.1) that forms an intermediate space and the intermediate space is divided into two ring spaces isolated gastight from one another including a first volume space (16) and a second volume space (17), the first volume space (16) being connected to the second gas-conducting line (14) and the second volume space (17) being connected to the first gas-conducting line (11), e) the first and second throttle valves (20, 21) each have a housing (36) comprising a receptacle space (33), into which a valve plug (25) is movable in such a manner that the flow cross-section of each line (11, 14) is completely unblocked when the plug is in the open position, and f) the first volume space (16) and the second volume space (17), in flow interaction with the functions of the plug (25) which completely unblocks the flow cross-section of each gas-conducting line (11, 14) in the open position of the plug (25), and permits a circulation of the cold gas with favorable flow to provide rapid cooling of the batch (7).
 4. The retort furnace according to claim 1 or 3, wherein the external diameter of the second floor (9.1) is dimensioned smaller than the internal diameter of the retort (3).
 5. The retort furnace according to claim 1 or 3, wherein the first volume space (16) has a flow connection with the second gas-conducting line (14) to an external coolant gas fan (13).
 6. The retort furnace according to claim 1 or 3, wherein the second volume space (17) has a flow connection with the first gas-conducting line (11) to an external cooler (12).
 7. The retort furnace according to claim 1 or 3, wherein the second volume space (17) is connected to suction pipes (19), which are connected to the treatment space (6) enclosed by the retort (3).
 8. The retort furnace according to claim 1 or 3, wherein the first volume space (16) and the second volume space (17) are formed as two concentric ring spaces isolated gastight from one another by a ring (18).
 9. The retort furnace according to claim 2 or 3, wherein the valve plug (25), which is movable into the receptacle space (33) of the housing (36) of each throttle valve (20, 21), has a pivot arm (22), which is connected to a holding arm (27) so it is pivotable around a pivot point (32).
 10. The retort furnace according to claim 9, wherein the pivot arm (22) is connected to the holding arm (27) so it is pivotable through an angle that is greater than about 90°.
 11. The retort furnace according to claim 9, wherein the pivot arm (22) is connected to a drive mechanism (28).
 12. The retort furnace according to claim 11, wherein the drive mechanism (28) comprises a pneumatic positioning cylinder.
 13. The retort furnace according to claim 2 or 3, wherein the housing (36) is removably connected to one of the gas-conducting lines (11, 14) using a first flange connection (23) and a second flange connection (24).
 14. The retort furnace according to claim 13, wherein the housing (36) has an installation opening (34), which is closable by means of a cover lid (35).
 15. The retort furnace according to claim 14, wherein the drive mechanism (28) is mounted on the cover lid (35) and has a piston rod (29) which extends through the cover lid (35) gastight, and which is linked to the pivot arm (22) using a coupling element (30) of the piston rod (29) and an oblong hole (30) of the pivot arm (22) to actuate the plug (25).
 16. The retort furnace according to claim 15, wherein the holding arm (27) is connected to the cover lid (35). 